Assumed audience
General adult who has completed Genetics and Evolution.
Levels of ecological organization
Individual → population → community → ecosystem → biome → biosphere. Each level has its own questions and dynamics.
Ecosystems
A community of organisms plus the nonliving components of their environment (ecosystem). Energy flows through ecosystems via food webs. Matter cycles through ecosystems via biogeochemical cycles (carbon, nitrogen, phosphorus, water).
Producers, consumers, decomposers
Photosynthetic organisms (plants, algae) capture solar energy. Herbivores eat producers; predators eat herbivores. Decomposers (primarily fungi and bacteria) break down dead matter and recycle nutrients.
Symbiosis
Organisms of different species living in close association (symbiosis). Mutualism (both benefit — mycorrhizal fungi and plants), parasitism (one benefits at the other’s expense), commensalism (one benefits, the other is unaffected).
Niche and habitat
A species’ niche is its role in the ecosystem — what it eats, what eats it, where it lives, how it interacts with others. A habitat is the physical place where an organism lives. See niche construction.
Biodiversity
The variety of life at all levels — genetic, species, ecosystem. Biodiversity enhances ecosystem stability, resilience, and productivity. Current biodiversity is threatened by habitat destruction, climate change, pollution, and invasive species.
Why this matters
Ecology connects the molecular and organismal levels of biology to the planetary scale. Understanding ecosystems explains why conservation matters, how human activity affects the biosphere, and how biological communities sustain themselves.